scripts/ext-tools.sh: set all prebuilt tool files to same timestamp

The GitHub CI was sometimes still building some tools again even when
the same version was already pre-built. This change fixes the problem
and should improve the speed of the GitHub CI actions. The duration of
the "Build tools" step will be reduced from 5 to 20 minutes down to
10 to 15 seconds.

make also checks that dependencies are not more recent than the target
it wants to build. Previously find returned files in an arbitrary order
and touch set the current timestamp. Since touch is called per file the
timestamps differ in fractional seconds, so not all files got the same
time. make detected a more recent dependency and started to rebuild.
Now all files are set to the same timestamp and make will assume
everything is up to date.

It is sufficient to only touch the stamp files to prevent rebuilding.

Link: https://github.com/openwrt/openwrt/pull/22888
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit cd6cb9f765df46eea7aefaab9d61e143c3996423)

scripts/ext-tools.sh

@@ -4,10 +4,6 @@ TOOLS_TAR=""
 HOST_BUILD_DIR=$(pwd)/"build_dir/host"
 HOST_STAGING_DIR_STAMP=$(pwd)/"staging_dir/host/stamp"
 
-refresh_timestamps() {
-	find -H "$1" -not -type l -print0 | xargs -0 touch
-}
-
 extract_prebuilt_tar() {
 	tar -xf "$1"
 }
@@ -18,15 +14,15 @@ refresh_prebuilt_tools() {
 		exit 1
 	fi
 
-	refresh_timestamps "$HOST_BUILD_DIR"
-	sleep 1
-
 	if [ ! -d "$HOST_STAGING_DIR_STAMP" ]; then
 		echo "Can't find Host Staging Dir Stamp "$HOST_STAGING_DIR_STAMP"" >&2
 		exit 1
 	fi
 
-	refresh_timestamps "$HOST_STAGING_DIR_STAMP"
+	local now
+	now=$(date +%Y%m%d%H%M.%S)
+	find -H "$HOST_BUILD_DIR" "$HOST_STAGING_DIR_STAMP" \
+		-type f -empty -print0 | xargs -0 touch -t "$now"
 
 	return 0
 }